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          LV04-03-文件操作-文件IO
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    <div class="post-body" itemprop="articleBody"><p>本文主要是C语言——文件I&#x2F;O基本操作的相关笔记，若笔记中有错误或者不合适的地方，欢迎批评指正😃。</p>
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<details class="folding-tag" blue><summary> 点击查看使用工具及版本 </summary>
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              <table>    <tr>        <td align="center" width=150px>Windows</td>        <td align="left">windows11</td>    </tr>    <tr>        <td align="center">Ubuntu</td>        <td align="left">Ubuntu16.04的64位版本</td>      </tr>    <tr>        <td align="center">VMware® Workstation 16 Pro</td>        <td align="left">16.2.3 build-19376536</td>      </tr>    <tr>        <td align="center">SecureCRT</td>        <td align="left">Version 8.7.2 (x64 build 2214)   -   正式版-2020年5月14日</td>      </tr>    <tr>        <td align="center">开发板</td>        <td align="left">正点原子 i.MX6ULL Linux阿尔法开发板</td>      </tr>    <tr>        <td align="center">uboot</td>        <td align="left">NXP官方提供的uboot，NXP提供的版本为uboot-imx-rel_imx_4.1.15_2.1.0_ga(使用的uboot版本为U-Boot 2016.03)</td>      </tr>    <tr>        <td align="center">linux内核</td>        <td align="left">linux-4.15(NXP官方提供)</td>      </tr>    <tr>        <td align="center">STM32开发板</td>        <td align="left">正点原子战舰V3(STM32F103ZET6)</td>      </tr></table>
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<details class="folding-tag" blue><summary> 点击查看本文参考资料 </summary>
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              <table>    <tr><td align="center">参考方向  </td><td align="center">参考原文</td></tr>    <tr><td align="left">---</td><td align="left"><a href="" target="_blank">--- <i class="fa fa-external-link-alt"></i> </a></td></tr></table>
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<h1 id="一、文件打开与关闭"><a href="#一、文件打开与关闭" class="headerlink" title="一、文件打开与关闭"></a><font size=3>一、文件打开与关闭</font></h1><h2 id="1-基本函数"><a href="#1-基本函数" class="headerlink" title="1. 基本函数"></a><font size=3>1. 基本函数</font></h2><h3 id="1-1-open"><a href="#1-1-open" class="headerlink" title="1.1 open()"></a><font size=3>1.1 open()</font></h3><p>在 linux 下可以使用 man 2 open 命令查看该函数的帮助手册。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;sys/types.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;sys/stat.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;fcntl.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 函数声明 */</span></span><br><span class="line"><span class="type">int</span> <span class="title function_">open</span><span class="params">(<span class="type">const</span> <span class="type">char</span> *pathname, <span class="type">int</span> flags)</span>;</span><br><span class="line"><span class="type">int</span> <span class="title function_">open</span><span class="params">(<span class="type">const</span> <span class="type">char</span> *pathname, <span class="type">int</span> flags, <span class="type">mode_t</span> mode)</span>;</span><br></pre></td></tr></table></figure>

<p><strong>【函数说明】</strong>该函数打开一个文件，获取文件描述符；打开文件时使用两个参数，创建文件时第三个参数指定新文件的权限。</p>
<p><strong>【函数参数】</strong></p>
<ul>
<li>pathname ：被打开的文件名（可包括路径名）。</li>
<li>flags ：表示打开文件所采用的操作。</li>
</ul>
<details class="folding-tag" blue><summary> 点击查看详细的 flag 常量 </summary>
              <div class='content'>
              <p>（1） flag  常量可取的值</p><table>    <tr><td align="center" width=150px>O_RDONLY</td><td align="left">只读方式打开文件。</td><td align="left" rowspan=3>这三个参数互斥</td></tr>    <tr><td align="center" width=150px>O_WRONLY</td><td align="left" >可写方式打开文件。</td></tr>    <tr><td align="center" width=150px>O_RDWR  </td><td align="left">读写方式打开文件。</td></tr>    <tr><td align="center" width=150px>O_CREAT </td><td align="left" colspan=2>如果该文件不存在，就创建一个新的文件，并用第三的参数为其设置权限。</td></tr>    <tr><td align="center" width=150px>O_EXCL  </td><td align="left" colspan=2>如果使用O_CREAT时文件存在，则可返回错误消息。这一参数可测试文件是否存在。</td></tr>    <tr><td align="center" width=150px>O_NOCTTY</td><td align="left" colspan=2>使用本参数时，如文件为终端，那么终端不可以作为调用open()系统调用的那个进程的控制终端。</td></tr>    <tr><td align="center" width=150px>O_TRUNC </td><td align="left" colspan=2>如文件已经存在，那么打开文件时先删除文件中原有数据。</td></tr>    <tr><td align="center" width=150px>O_APPEND</td><td align="left" colspan=2>以添加方式打开文件，所以对文件的写操作都在文件的末尾进行。</td></tr></table><p>【注意】前三个参数必须指定，且只能指定一个，后边的几个可以与前边搭配使用。</p><p>（2） flag 常量与标准 I&#x2F;O 文件打开权限关系、</p><table>    <tr><td align="center" width=150px>r </td><td align="left" colspan=2>O_RDONLY</td></tr>    <tr><td align="center" width=150px>r+</td><td align="left" colspan=2>O_RDWR</td></tr>    <tr><td align="center" width=150px>w </td><td align="left" colspan=2>O_WRONLY | O_CREAT | O_TRUNC, 0664</td></tr>    <tr><td align="center" width=150px>w+</td><td align="left" colspan=2>O_RDWR | O_CREAT | O_TRUNC, 0664</td></tr>    <tr><td align="center" width=150px>a </td><td align="left" colspan=2>O_WRONLY | O_CREAT | O_APPEND, 0664</td></tr>    <tr><td align="center" width=150px>a+</td><td align="left" colspan=2>O_RDWR | O_CREAT | O_APPEND, 0664</td></tr></table>
              </div>
            </details>

<ul>
<li>mode ：表示被打开文件的存取权限，为 8 进制表示法。此参数<strong>只有在建立新文件时有效</strong>。新建文件时的权限会受到 umask  值影响，实际权限是 mode - umaks</li>
</ul>
<details class="folding-tag" blue><summary> 点击查看什么是 umask </summary>
              <div class='content'>
              <p>在类 unix 系统中， umask 是确定掩码设置的命令，该掩码用来设定文件或目录的初始权限。 umask 确定了文件创建时的初始权限:</p><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">文件或目录的初始权限 = 文件或目录的最大默认权限 - umask权限</span><br></pre></td></tr></table></figure><p>文件初始默认权限为 0666 ，目录为 0777 ，若用户 umask 为 0002 ，则新创建的文件或目录在没有指定的情况下默认权限分别为 0664 、 0775 )。</p><p>在 Linux 下，我们可以使用 umask 命令来查看当前用户默认的 umask 值，同时也可以在 umask 命令后面跟上需要设置的 umask 值来重新设置 umask 。</p>
              </div>
            </details>

<p><strong>【返回值】</strong> 返回值是一个 int 类型，成功时返回文件描述符(非负整数)；出错时返回 EOF 。</p>
<p><strong>【使用格式】</strong>一般情况下基本使用格式如下：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需要包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;sys/types.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;sys/stat.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;fcntl.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 至少应该有的语句 */</span></span><br><span class="line"><span class="type">int</span> fd;<span class="comment">/* 接收文件描述符 */</span></span><br><span class="line"><span class="comment">/* 以只写方式打开文件01open_close.txt。如果文件不存在则创建，如果文件存在则清空 */</span></span><br><span class="line">fd = open(<span class="string">&quot;01open_close.txt&quot;</span>, O_WRONLY | O_CREAT | O_TRUNC, <span class="number">0666</span>);</span><br></pre></td></tr></table></figure>

<p><strong>【注意事项】</strong> 该函数可以打开设备文件，但是不<strong>能创建设备文件</strong>。</p>
<h3 id="1-2-close"><a href="#1-2-close" class="headerlink" title="1.2 close()"></a><font size=3>1.2 close()</font></h3><p>在 linux 下可以使用 man 2 close 命令查看该函数的帮助手册。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;unistd.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 函数声明 */</span></span><br><span class="line"><span class="type">int</span> <span class="title function_">close</span><span class="params">(<span class="type">int</span> fd)</span>;</span><br></pre></td></tr></table></figure>

<p><strong>【函数说明】</strong>该函数关闭一个打开的文件。</p>
<p><strong>【函数参数】</strong></p>
<ul>
<li>fd ：已打开文件的文件描述符。</li>
</ul>
<p><strong>【返回值】</strong> 返回值是一个整数，成功时返回 0 ；出错时返回 EOF 。</p>
<p><strong>【使用格式】</strong>一般情况下基本使用格式如下：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需要包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;unistd.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 至少应该有的语句 */</span></span><br><span class="line"><span class="type">int</span> ret;<span class="comment">/* 保存文件关闭返回值 */</span></span><br><span class="line">ret = close(fd);</span><br></pre></td></tr></table></figure>

<p><strong>【注意事项】</strong> </p>
<p>（1）程序结束时自动关闭所有打开的文件。</p>
<p>（2）文件关闭后，文件描述符不再代表文件。</p>
<h2 id="2-使用实例"><a href="#2-使用实例" class="headerlink" title="2. 使用实例"></a><font size=3>2. 使用实例</font></h2><details class="folding-tag" blue><summary> 点击查看实例 </summary>
              <div class='content'>
              <figure class="highlight c"><figcaption><span>test.c</span></figcaption><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/** =====================================================</span></span><br><span class="line"><span class="comment"> * Copyright © hk. 2022-2022. All rights reserved.</span></span><br><span class="line"><span class="comment"> * File name: 01open_close.c</span></span><br><span class="line"><span class="comment"> * Author   : fanhua</span></span><br><span class="line"><span class="comment"> * Description: 文件IO——文件打开关闭</span></span><br><span class="line"><span class="comment"> * ======================================================</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="comment">/* 头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="comment">/* read write close函数 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;unistd.h&gt;</span></span></span><br><span class="line"><span class="comment">/* open 函数 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;sys/types.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;sys/stat.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;fcntl.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="type">int</span> <span class="title function_">main</span><span class="params">(<span class="type">int</span> argc,<span class="type">char</span>*argv[])</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="type">int</span> fd;<span class="comment">/* 接收文件描述符 */</span></span><br><span class="line">	<span class="type">int</span> ret;<span class="comment">/* 保存文件关闭返回值 */</span></span><br><span class="line">	<span class="comment">/* 1. 打开文件 man 2 open*/</span></span><br><span class="line">	fd = open(<span class="string">&quot;01open_close.txt&quot;</span>, O_WRONLY | O_CREAT | O_TRUNC, <span class="number">0666</span>);</span><br><span class="line">	<span class="comment">/* 2. 判断是否打开成功 */</span></span><br><span class="line">	<span class="keyword">if</span>(fd &lt; <span class="number">0</span>)</span><br><span class="line">	&#123;</span><br><span class="line">		<span class="built_in">printf</span>(<span class="string">&quot;open file err\n&quot;</span>);</span><br><span class="line">		<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">else</span></span><br><span class="line">	&#123;</span><br><span class="line">		<span class="built_in">printf</span>(<span class="string">&quot;sucess,fd=%d\n&quot;</span>,fd);</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="comment">/* 3. 关闭文件 */</span></span><br><span class="line">	ret = close(fd);</span><br><span class="line">    <span class="keyword">if</span>(ret &lt; <span class="number">0</span>)</span><br><span class="line">	&#123;</span><br><span class="line">        <span class="built_in">printf</span>(<span class="string">&quot;close failed\n&quot;</span>);</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    ret = close(fd);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;ret=%d\n&quot;</span>, ret);</span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br><span class="line"></span><br></pre></td></tr></table></figure>
              </div>
            </details>

<p>在终端执行以下命令编译程序：</p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">gcc test.c -Wall # 生成可执行文件 a.out </span><br><span class="line">./a.out # 执行可执行程序</span><br></pre></td></tr></table></figure>

<h1 id="二、文件读写"><a href="#二、文件读写" class="headerlink" title="二、文件读写"></a><font size=3>二、文件读写</font></h1><h2 id="1-基本函数-1"><a href="#1-基本函数-1" class="headerlink" title="1. 基本函数"></a><font size=3>1. 基本函数</font></h2><h3 id="1-1-read"><a href="#1-1-read" class="headerlink" title="1.1 read()"></a><font size=3>1.1 read()</font></h3><p>在 linux 下可以使用 man 2 read 命令查看该函数的帮助手册。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;unistd.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 函数声明 */</span></span><br><span class="line"><span class="type">ssize_t</span> <span class="title function_">read</span><span class="params">(<span class="type">int</span> fd, <span class="type">void</span> *buf, <span class="type">size_t</span> count)</span>;</span><br></pre></td></tr></table></figure>

<p><strong>【函数说明】</strong>该函数从文件中读取数据。</p>
<p><strong>【函数参数】</strong></p>
<ul>
<li>fd ：文件描述符。</li>
<li>buf ：接收数据的缓冲区。</li>
<li>count ：需要读取的字节数，不应超过 buf 。</li>
</ul>
<p><strong>【返回值】</strong> 返回值是 ssize_t 类型（表示有符号的 size_t ），成功时返回实际读取的字节数；出错时返回 EOF ，读到文件末尾时返回 0 。</p>
<details class="folding-tag" blue><summary> 点击查看 EOF 说明 </summary>
              <div class='content'>
              <p>EOF  是  end of file  的缩写，表示文件末尾，是在  stdio.h  中定义的宏，它的值是一个负数，往往是  -1 ，但是不绝对是  -1 ，也可以是其他负数，这要看编译器的规定。</p>
              </div>
            </details>

<p><strong>【使用格式】</strong>一般情况下基本使用格式如下：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需要包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;unistd.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 至少应该有的语句 */</span></span><br><span class="line"><span class="type">int</span> fd;</span><br><span class="line"><span class="type">char</span> buff[<span class="number">32</span>]=&#123;<span class="number">0</span>&#125;;</span><br><span class="line"><span class="type">int</span> ret;</span><br><span class="line">fd = open(<span class="string">&quot;02read_write.txt&quot;</span>,O_RDWR | O_CREAT | O_APPEND, <span class="number">0666</span>);</span><br><span class="line">ret = read(fd, buff, <span class="number">32</span>);</span><br></pre></td></tr></table></figure>

<p><strong>【注意事项】</strong></p>
<p>（1）读取过程中，未读完 count 字节时，若遇到换行，则会一起读取。</p>
<p>（2）对于⼀个数组，总是要自动分配⼀个 ‘\0’ 作为结束，所以实际有效的 buf 长度就成为 sizeof(buf) - 1 了，最好就是在读取完成后自己加上一个 ‘\0’ ，以防止后边打印出现乱码的情况。</p>
<h3 id="1-2-write"><a href="#1-2-write" class="headerlink" title="1.2 write()"></a><font size=3>1.2 write()</font></h3><p>在 linux 下可以使用 man 2 write 命令查看该函数的帮助手册。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;unistd.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 函数声明 */</span></span><br><span class="line"><span class="type">ssize_t</span> <span class="title function_">write</span><span class="params">(<span class="type">int</span> fd, <span class="type">const</span> <span class="type">void</span> *buf, <span class="type">size_t</span> count)</span>;</span><br></pre></td></tr></table></figure>

<p><strong>【函数说明】</strong>该函数向文件写入数据。</p>
<p><strong>【函数参数】</strong></p>
<ul>
<li><p>fd ：文件描述符。</p>
</li>
<li><p>buf ：要写入文件的数据的缓冲区。</p>
</li>
<li><p>count ：需要写入的字节数，不应超过 buf 。</p>
</li>
</ul>
<p><strong>【返回值】</strong>返回值是一个 ssize_t 类型，成功时返回实际写入的字节数；出错时返回 EOF 。</p>
<p><strong>【使用格式】</strong>一般情况下基本使用格式如下：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需要包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;unistd.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 至少应该有的语句 */</span></span><br><span class="line"><span class="type">int</span> fd;</span><br><span class="line"><span class="type">char</span> buff[<span class="number">32</span>]= <span class="string">&quot;fanhualuojin&quot;</span>;</span><br><span class="line"><span class="type">int</span> ret;</span><br><span class="line">fd = open(<span class="string">&quot;02read_write.txt&quot;</span>,O_RDWR | O_CREAT | O_APPEND, <span class="number">0666</span>);</span><br><span class="line">ret = write(fd, buff, <span class="built_in">strlen</span>(buff));</span><br></pre></td></tr></table></figure>

<p><strong>【注意事项】</strong> 数据写入完毕后，文件指针指向文件尾部，此时直接读取文件，则什么也读不到，可以使用后边的函数移动指针，再进行读取。</p>
<h2 id="2-使用实例-1"><a href="#2-使用实例-1" class="headerlink" title="2. 使用实例"></a><font size=3>2. 使用实例</font></h2><details class="folding-tag" blue><summary> 点击查看实例 </summary>
              <div class='content'>
              <figure class="highlight c"><figcaption><span>test.c</span></figcaption><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/** =====================================================</span></span><br><span class="line"><span class="comment"> * Copyright © hk. 2022-2022. All rights reserved.</span></span><br><span class="line"><span class="comment"> * File name: 02read_write.c</span></span><br><span class="line"><span class="comment"> * Author   : fanhua</span></span><br><span class="line"><span class="comment"> * Description: 文件IO——文件读写</span></span><br><span class="line"><span class="comment"> * ======================================================</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="comment">/* 头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="comment">/* read write close函数 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;unistd.h&gt;</span></span></span><br><span class="line"><span class="comment">/* open 函数 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;sys/types.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;sys/stat.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;fcntl.h&gt;</span></span></span><br><span class="line"><span class="comment">/* strlen 函数 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;string.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="type">void</span> <span class="title function_">test_read</span><span class="params">()</span>;</span><br><span class="line"><span class="type">void</span> <span class="title function_">test_write</span><span class="params">()</span>;</span><br><span class="line"></span><br><span class="line"><span class="type">int</span> <span class="title function_">main</span><span class="params">(<span class="type">int</span> argc,<span class="type">char</span>*argv[])</span></span><br><span class="line">&#123;</span><br><span class="line">	test_read();</span><br><span class="line">	<span class="comment">// test_write();</span></span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * @Function: ssize_t  read(int fd, void *buf, size_t count);</span></span><br><span class="line"><span class="comment"> * @Description: 成功时返回实际读取的字节数；出错时返回EOF</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">void</span> <span class="title function_">test_read</span><span class="params">()</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="comment">/* 定义一个文件描述符变量 */</span></span><br><span class="line">	<span class="type">int</span> fd;</span><br><span class="line">	<span class="type">char</span> buff[<span class="number">32</span>]=&#123;<span class="number">0</span>&#125;;</span><br><span class="line">	<span class="type">int</span> ret;</span><br><span class="line">	<span class="comment">/* 1. 打开当前路径下文件 */</span></span><br><span class="line">	fd = open(<span class="string">&quot;02read_write.txt&quot;</span>,O_RDWR | O_CREAT | O_APPEND, <span class="number">0666</span>);</span><br><span class="line">	<span class="comment">/* 2. 判断是否打开成功 */</span></span><br><span class="line">	<span class="keyword">if</span>(fd &lt; <span class="number">0</span>)</span><br><span class="line">	&#123;</span><br><span class="line">		<span class="built_in">printf</span>(<span class="string">&quot;open file err\n&quot;</span>);</span><br><span class="line">		<span class="keyword">return</span>;</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">else</span></span><br><span class="line">	&#123;</span><br><span class="line">		<span class="built_in">printf</span>(<span class="string">&quot;sucess,fd=%d\n&quot;</span>,fd);</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="comment">/* 3. 读取文件内容 */</span></span><br><span class="line">	ret = read(fd, buff, <span class="number">32</span>);</span><br><span class="line">	<span class="keyword">if</span>(ret &lt; <span class="number">0</span>)</span><br><span class="line">	&#123;</span><br><span class="line">		perror(<span class="string">&quot;read&quot;</span>);</span><br><span class="line">		close(fd);</span><br><span class="line">		<span class="keyword">return</span>;</span><br><span class="line">	&#125;</span><br><span class="line">	buff[<span class="number">31</span>] = <span class="number">0</span>;</span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;read buff=%s\n&quot;</span>, buff);</span><br><span class="line">	<span class="comment">/* 4. 关闭文件 */</span></span><br><span class="line">	close(fd);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * @Function: ssize_t  write(int fd, void *buf, size_t count);</span></span><br><span class="line"><span class="comment"> * @Description: 成功时返回实际写入的字节数；出错时返回EOF</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">void</span> <span class="title function_">test_write</span><span class="params">()</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="comment">/* 定义一个文件描述符变量 */</span></span><br><span class="line">	<span class="type">int</span> fd;</span><br><span class="line">	<span class="type">char</span> buff[<span class="number">32</span>]= <span class="string">&quot;fanhualuojin&quot;</span>;</span><br><span class="line">	<span class="type">char</span> a[<span class="number">32</span>];</span><br><span class="line">	<span class="type">int</span> ret;</span><br><span class="line">	<span class="comment">/* 1. 打开当前路径下文件 */</span></span><br><span class="line">	fd = open(<span class="string">&quot;02read_write.txt&quot;</span>,O_RDWR | O_CREAT | O_APPEND, <span class="number">0666</span>);</span><br><span class="line">	<span class="comment">/* 2. 判断是否打开成功 */</span></span><br><span class="line">	<span class="keyword">if</span>(fd &lt; <span class="number">0</span>)</span><br><span class="line">	&#123;</span><br><span class="line">		<span class="built_in">printf</span>(<span class="string">&quot;open file err\n&quot;</span>);</span><br><span class="line">		<span class="keyword">return</span>;</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">else</span></span><br><span class="line">	&#123;</span><br><span class="line">		<span class="built_in">printf</span>(<span class="string">&quot;sucess,fd=%d\n&quot;</span>,fd);</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="comment">/* 3. 写入文件内容 */</span></span><br><span class="line">	ret = write(fd, buff, <span class="built_in">strlen</span>(buff));</span><br><span class="line">	<span class="keyword">if</span>(ret &lt; <span class="number">0</span>)</span><br><span class="line">	&#123;</span><br><span class="line">		perror(<span class="string">&quot;write&quot;</span>);</span><br><span class="line">		close(fd);</span><br><span class="line">		<span class="keyword">return</span>;</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sucess,write count=%d\n&quot;</span>,ret);</span><br><span class="line">	<span class="comment">/* 4. 读取文件内容,这里会发现什么也读不到，可以看下一个例子，这里还仅仅是测试写入函数 */</span></span><br><span class="line">	ret = read(fd , a, <span class="number">32</span>);</span><br><span class="line">	<span class="keyword">if</span>(ret &lt; <span class="number">0</span>)</span><br><span class="line">	&#123;</span><br><span class="line">		perror(<span class="string">&quot;read&quot;</span>);</span><br><span class="line">		close(fd);</span><br><span class="line">		<span class="keyword">return</span>;</span><br><span class="line">	&#125;</span><br><span class="line">	a[<span class="number">31</span>] = <span class="number">0</span>;</span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;read buff=%s\n&quot;</span>, a);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;read count=%d\n&quot;</span>,ret);</span><br><span class="line">	<span class="comment">/* 5. 关闭文件 */</span></span><br><span class="line">	close(fd);</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
              </div>
            </details>

<p>在终端执行以下命令编译程序：</p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">gcc test.c -Wall # 生成可执行文件 a.out </span><br><span class="line">./a.out # 执行可执行程序</span><br></pre></td></tr></table></figure>

<h1 id="三、文件定位"><a href="#三、文件定位" class="headerlink" title="三、文件定位"></a><font size=3>三、文件定位</font></h1><h2 id="1-lseek"><a href="#1-lseek" class="headerlink" title="1. lseek()"></a><font size=3>1. lseek()</font></h2><p>在 linux 下可以使用 man 2 lseek 命令查看该函数的帮助手册。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;sys/types.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;unistd.h&gt;</span></span></span><br><span class="line"><span class="comment">/* 函数声明 */</span></span><br><span class="line"><span class="type">off_t</span> <span class="title function_">lseek</span><span class="params">(<span class="type">int</span> fd, <span class="type">off_t</span> offset, intt whence)</span>;</span><br></pre></td></tr></table></figure>

<p><strong>【函数说明】</strong>该函数用于读写文件时偏移文件指针，定位读写位置。</p>
<p><strong>【函数参数】</strong></p>
<ul>
<li><p>fd ：文件描述符。</p>
</li>
<li><p>offset ：相对于 whence （基准）的偏移量。</p>
</li>
<li><p>whence ：添加偏移  offset  的位置。</p>
</li>
</ul>
<details class="folding-tag" blue><summary> 点击查看 whence 参数 </summary>
              <div class='content'>
              <table>    <tr><td align="center" width=150px>常量</td><td align="left">描述</td></tr>    <tr><td align="center" width=150px>SEEK_SET</td><td align="left">文件的开头</td></tr>    <tr><td align="center" width=150px>SEEK_CUR</td><td align="left">文件指针的当前位置</td></tr>    <tr><td align="center" width=150px>SEEK_END</td><td align="left">文件的末尾</td></tr></table>
              </div>
            </details>

<p><strong>【返回值】</strong>返回值是 off_t 类型，成功时返回当前的文件读写位置；出错时返回 EOF 。</p>
<p><strong>【使用格式】</strong>一般情况下基本使用格式如下：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需要包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;sys/types.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;unistd.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 至少应该有的语句 */</span></span><br><span class="line">lseek(fd, <span class="number">0</span>, SEEK_SET);</span><br></pre></td></tr></table></figure>

<p><strong>【注意事项】</strong>lseek()允许将文件偏移量设置在文件末尾之外(但这不会改变文件的大小)。如果稍后在此时写入数据，则后续读取间隙( a “hole”)中的数据将返回空字节(‘\0’)，直到读到数据实际写入的位置为止。</p>
<h2 id="2-使用实例-2"><a href="#2-使用实例-2" class="headerlink" title="2. 使用实例"></a><font size=3>2. 使用实例</font></h2><details class="folding-tag" blue><summary> 点击查看实例 </summary>
              <div class='content'>
              <figure class="highlight c"><figcaption><span>test.c</span></figcaption><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br><span class="line">115</span><br><span class="line">116</span><br><span class="line">117</span><br><span class="line">118</span><br><span class="line">119</span><br><span class="line">120</span><br><span class="line">121</span><br><span class="line">122</span><br><span class="line">123</span><br><span class="line">124</span><br><span class="line">125</span><br><span class="line">126</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/** =====================================================</span></span><br><span class="line"><span class="comment"> * Copyright © hk. 2022-2022. All rights reserved.</span></span><br><span class="line"><span class="comment"> * File name: 03lseek.c</span></span><br><span class="line"><span class="comment"> * Author   : fanhua</span></span><br><span class="line"><span class="comment"> * Description: 文件IO——文件读写</span></span><br><span class="line"><span class="comment"> * ======================================================</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="comment">/* 头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;stdio.h&gt;</span></span></span><br><span class="line"><span class="comment">/* read write close函数 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;unistd.h&gt;</span></span></span><br><span class="line"><span class="comment">/* open 函数 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;sys/types.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;sys/stat.h&gt;</span></span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;fcntl.h&gt;</span></span></span><br><span class="line"><span class="comment">/* strlen 函数 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;string.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="type">void</span> <span class="title function_">test_none_lseek</span><span class="params">()</span>;</span><br><span class="line"><span class="type">void</span> <span class="title function_">test_lseek</span><span class="params">()</span>;</span><br><span class="line"></span><br><span class="line"><span class="type">int</span> <span class="title function_">main</span><span class="params">(<span class="type">int</span> argc,<span class="type">char</span>*argv[])</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="comment">// test_none_lseek();</span></span><br><span class="line">	test_lseek();</span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * @Function: </span></span><br><span class="line"><span class="comment"> * @Description: 写入数据后，直接读取，会发现什么也读不到，原因就在于写入完毕后，文件指针移动到了文件末尾。</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">void</span> <span class="title function_">test_none_lseek</span><span class="params">()</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="comment">/* 定义一个文件描述符变量 */</span></span><br><span class="line">	<span class="type">int</span> fd;</span><br><span class="line">	<span class="type">char</span> buff[<span class="number">32</span>]= <span class="string">&quot;fanhualuojin&quot;</span>;</span><br><span class="line">	<span class="type">char</span> a[<span class="number">32</span>];</span><br><span class="line">	<span class="type">int</span> ret;</span><br><span class="line">	<span class="comment">/* 1. 打开当前路径下文件 */</span></span><br><span class="line">	fd = open(<span class="string">&quot;03lseek.txt&quot;</span>,O_RDWR | O_CREAT | O_APPEND, <span class="number">0666</span>);</span><br><span class="line">	<span class="comment">/* 2. 判断是否打开成功 */</span></span><br><span class="line">	<span class="keyword">if</span>(fd &lt; <span class="number">0</span>)</span><br><span class="line">	&#123;</span><br><span class="line">		<span class="built_in">printf</span>(<span class="string">&quot;open file err\n&quot;</span>);</span><br><span class="line">		<span class="keyword">return</span>;</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">else</span></span><br><span class="line">	&#123;</span><br><span class="line">		<span class="built_in">printf</span>(<span class="string">&quot;sucess,fd=%d\n&quot;</span>,fd);</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="comment">/* 3. 写入文件内容 */</span></span><br><span class="line">	ret = write(fd, buff, <span class="built_in">strlen</span>(buff));</span><br><span class="line">	<span class="keyword">if</span>(ret &lt; <span class="number">0</span>)</span><br><span class="line">	&#123;</span><br><span class="line">		perror(<span class="string">&quot;write&quot;</span>);</span><br><span class="line">		close(fd);</span><br><span class="line">		<span class="keyword">return</span>;</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sucess,write count=%d\n&quot;</span>,ret);</span><br><span class="line">	<span class="comment">/* 4. 读取文件内容 */</span></span><br><span class="line">	ret = read(fd , a, <span class="number">32</span>);</span><br><span class="line">	<span class="keyword">if</span>(ret &lt; <span class="number">0</span>)</span><br><span class="line">	&#123;</span><br><span class="line">		perror(<span class="string">&quot;read&quot;</span>);</span><br><span class="line">		close(fd);</span><br><span class="line">		<span class="keyword">return</span>;</span><br><span class="line">	&#125;</span><br><span class="line">	a[<span class="number">31</span>] = <span class="number">0</span>;</span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;read buff=%s\n&quot;</span>, a);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;read count=%d\n&quot;</span>,ret);</span><br><span class="line">	<span class="comment">/* 5. 关闭文件 */</span></span><br><span class="line">	close(fd);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * @Function: off_t lseek(int fd, off_t offset, intt whence);</span></span><br><span class="line"><span class="comment"> * @Description: 成功时返回实际写入的字节数；出错时返回EOF</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">void</span> <span class="title function_">test_lseek</span><span class="params">()</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="comment">/* 定义一个文件描述符变量 */</span></span><br><span class="line">	<span class="type">int</span> fd;</span><br><span class="line">	<span class="type">char</span> buff[<span class="number">32</span>]= <span class="string">&quot;fanhualuojin&quot;</span>;</span><br><span class="line">	<span class="type">char</span> a[<span class="number">33</span>];</span><br><span class="line">	<span class="type">int</span> ret;</span><br><span class="line">	<span class="comment">/* 1. 打开当前路径下文件 */</span></span><br><span class="line">	fd = open(<span class="string">&quot;03lseek.txt&quot;</span>,O_RDWR | O_CREAT | O_APPEND, <span class="number">0666</span>);</span><br><span class="line">	<span class="comment">/* 2. 判断是否打开成功 */</span></span><br><span class="line">	<span class="keyword">if</span>(fd &lt; <span class="number">0</span>)</span><br><span class="line">	&#123;</span><br><span class="line">		<span class="built_in">printf</span>(<span class="string">&quot;open file err\n&quot;</span>);</span><br><span class="line">		<span class="keyword">return</span>;</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">else</span></span><br><span class="line">	&#123;</span><br><span class="line">		<span class="built_in">printf</span>(<span class="string">&quot;sucess,fd=%d\n&quot;</span>,fd);</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="comment">/* 3. 写入文件内容 */</span></span><br><span class="line">	ret = write(fd, buff, <span class="built_in">strlen</span>(buff));</span><br><span class="line">	<span class="keyword">if</span>(ret &lt; <span class="number">0</span>)</span><br><span class="line">	&#123;</span><br><span class="line">		perror(<span class="string">&quot;write&quot;</span>);</span><br><span class="line">		close(fd);</span><br><span class="line">		<span class="keyword">return</span>;</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;sucess,write count=%d\n&quot;</span>,ret);</span><br><span class="line">	</span><br><span class="line">	<span class="comment">/* 4. 设置文件指针位置 */</span></span><br><span class="line">	lseek(fd, <span class="number">0</span>, SEEK_SET);</span><br><span class="line">	</span><br><span class="line">	<span class="comment">/* 5. 读取文件内容 */</span></span><br><span class="line">	ret = read(fd, a, <span class="number">33</span>);</span><br><span class="line">	<span class="keyword">if</span>(ret &lt; <span class="number">0</span>)</span><br><span class="line">	&#123;</span><br><span class="line">		perror(<span class="string">&quot;read&quot;</span>);</span><br><span class="line">		close(fd);</span><br><span class="line">		<span class="keyword">return</span>;</span><br><span class="line">	&#125;</span><br><span class="line">	a[<span class="keyword">sizeof</span>(a)<span class="number">-1</span>] = <span class="number">0</span>;<span class="comment">/* 设置字符串结束标志，防止乱码 */</span></span><br><span class="line">    <span class="built_in">printf</span>(<span class="string">&quot;read buff=%s\n&quot;</span>, a);</span><br><span class="line">	<span class="built_in">printf</span>(<span class="string">&quot;read count=%d\n&quot;</span>,ret);</span><br><span class="line">	<span class="comment">/* 6. 关闭文件 */</span></span><br><span class="line">	close(fd);</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
              </div>
            </details>

<p>在终端执行以下命令编译程序：</p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">gcc test.c -Wall # 生成可执行文件 a.out </span><br><span class="line">./a.out # 执行可执行程序</span><br></pre></td></tr></table></figure>


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